1. Field of the Invention
The present invention relates to an image-pickup signal processor and a method of detecting flicker that, when taking pictures of objects by various types of image-pickup apparatuses, can effectively detect flickering of the images which is caused by frequency variation due to the power supply frequency of illuminating light rays and that can contribute to flicker elimination.
2. Description of the Related Art
So-called CMOS image sensors have hitherto been available.
In the CMOS image sensor, an image pickup area is formed by disposing a large number of photo sensors corresponding to image pickup pixels in a matrix pattern. The CMOS image sensor also has gating circuits for selectively reading out signal charges from the corresponding photo sensors. The gating circuit comprises a plurality of MOS transistors and is disposed at each pixel. Address scanners, which activate the gating circuit for the corresponding pixel and control the readout of the signal charges, are arranged in the vertical and horizontal directions in the CMOS image sensor.
In addition, the CMOS image sensor has shutter scanners accompanying the address scanners. The shutter scanner has an electronic shutter function that cancels signal charges remaining in the photo sensors prior to the charge storage time.
When an object is photographed using an image pickup apparatus that utilizes such a CMOS image sensor, for example, under a fluorescent lamp, the light rays of the fluorescent lamp include variations in the amount of light due to the frequency of the commercial power supply, which may appear as horizontal-striped flickering during image pick-up.
In order to solve this problem, various methods for detecting variations in the illuminating light rays, correcting picture signals by detecting signals, and eliminating flicker have been suggested.
However, in most of the known methods for correcting flicker, some kind of sensor for detecting flicker is used in the CMOS image sensor to electrically eliminate the flicker using the output of the sensor.